Hippocampal microcircuits are comprised of excitatory pyramidal cells, which integrate information and innervate downstream brain regions, and inhibitory interneurons, which function locally to regulate pyramidal cell activity and synchronicity. In the ventral hippocampus (vHipp), microcircuit dysfunction has been associated with a variety of neurological disorders, including neurodegenerative diseases, neurodevelopmental disorders, and psychiatric illnesses. Previous work has demonstrated that vHipp pyramidal cells differentially regulate schizophrenia-like behaviors depending on their downstream target. Similarly, unique classes of inhibitory interneurons (namely parvalbumin (PV)-positive and somatostatin(SST)-positive) also differently regulate schizophrenia-like behaviors. Therefore, the hypothesis of the current proposal is that PV- and SST-positive interneurons differentially regulate the function of ventral hippocampus pyramidal cells depending on their projection target. In the first aim, mammalian reconstitution across synaptic partners (mGRASP) will be used to test the hypothesis that PV- and SST-positive interneurons differentially innervate vHipp pyramidal cells depending on their target (i.e. the NAc or mPFC). In the second aim, fiber photometry, in vivo electrophysiology, and optogenetics will be used to test the functional regulation of NAc vs mPFC projecting vHipp neurons by PV- and SST-positive interneurons. Aim 3 will determine if microcircuit anatomy and function are altered by chronic stress, a predisposing factor for many neurological disorders. In line with the goals of the BRAIN Initiative, the results will provide insight into basic principles of neural circuit function and may lead to new strategies for the treatment and prevention of devastating neurological disorders. My long-term goal is to become an independent scientist that studies the neurobiological mechanisms underlying psychiatric disorders so that new and more effective treatments can be developed. The research plan described above will be supplemented by a career development plan that will allow me to gain the skills necessary to achieve this goal. Specifically, I have assembled a team of mentors from both in and outside of my institution to provide scientific training and career guidance. Further, I will attend local and national conferences, workshops, and meetings to enhance my training and ensure that I gain the skills requisite of an independent investigator. Together, this award will provide me with scientific training and career development opportunities, and importantly it will allow me to establish my own, independent line of research, which will focus on the effect of chronic stress on vHipp microcircuits.